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METEOROLOGY
ECVS IN THE STRATOSPHERE
O3, H2O, AEROSOL, N2O, CH4, CFCS, HCFCS, HFCS, SF6, PFCS, AND TEMPERATURE
Michaela I. Hegglin, University of Reading UK
GCOS COMPOSITION ECVs EXTEND INTO THE
STRATOSPHERE
http://www.wmo.int/pages/prog/gcos/index.php?name=EssentialClimateVariables#footnote4
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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GCOS COMPOSITION ECVs EXTEND INTO THE
STRATOSPHERE
New definition of stratospheric ECVs:
High-vertical resolution ozone, water vapour, aerosol, transport tracers
and temperature from the upper troposphere to the stratopause.
http://www.wmo.int/pages/prog/gcos/index.php?name=EssentialClimateVariables#footnote4
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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OBSERVATIONS
TES
solar occultation
•  Golden age of past limb satellite
observations that is ready for
exploitation.
Aura
SMILES
stellar occultation
limb emission
HIRDLS
limb scattering
MLS
nadir
ISS
Aura
Aura
ACE−MAESTRO
SCISAT−1
ACE−FTS
SCISAT−1
SCIAMACHY
Envisat
GOMOS
Envisat
MIPAS
Envisat
Meteor−3M
SAGE III
SMR
•  SPARC Data Initiative provided
first comprehensive
intercomparison of US and
European instruments.
Odin
OSIRIS
Odin
POAM III
POAM II
SPOT−4
SPOT−3
MLS
UARS
HALOE
UARS
SAGE II
SAGE I
LIMS
1975
ERBS
AEM−B
Nimbus 7
1980
1985
1990
1995
2000
2005
2010
•  No future satellite limb sounders
with the capability to measure
long-lived GHGs are foreseen for
the future.
•  Ground-based (e.g. NDACC)
observations have limited spatial
and temporal coverage, and
coarse vertical resolution.
SPARC Data Initiative Report
(Eds. Hegglin & Tegtmeier), in print
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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STRATOSPHERIC ECVs AND CLIMATE
•  Long-lived GHGs in the stratosphere affect both local temperatures and
surface climate ! IPCC
~Altitude (km)
Water vapour increase
Methane increase
Ozone increase
35
3
35
3
30
30
30
25
25
25
20
20
20
15
15
15
10
10
10
5
5
5
0
0
tropopause
-50
0
50
Latitude (degrees)
00
3
-50
0
50
Latitude (degrees)
35
0
0
-0.8 -0.6 -0.4 -0.2 -0.1 0.1 0.2 0.4 0.6 0.8
Relative Radiative Forcing
-50
0
50
Latitude (degrees)
ESA PREMIER:
Report for mission
selection, 2013
•  GHGs contribute to warming of surface climate (and aerosols to cooling).
•  In the stratosphere, most GHGs lead to a local cooling.
•  Dynamical feedbacks from chemistry-climate coupling extend to the surface (e.g.,
Antarctic ozone hole impact on Southern hemisphere surface climate during summer).
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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STRATOSPHERIC ECVs AND OZONE
•  GHGs from tropospheric sources are destroyed in the stratosphere,
affect chemistry, and impact the natural balance of the ozone layer.
! WMO/UNEP ozone assessment
•  Future mix of GHG emissions
will determine the future state
of the ozone layer (with CH4
and N2O having opposing
effects on stratospheric ozone
chemistry).
•  Transport of GHGs through the
stratosphere determines their
lifetimes.
•  Lifetimes of GHGs can be
derived from vertical
gradients (SPARC Lifetimes
Report, 2014)
Hegglin et al., WMO 2015; after Fleming et al., 2013
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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STRATOSPHERIC AEROSOL
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Hegglin et al., in preparation
SAGE II
HALOE
POAM II
POAM III
OSIRIS
SAGE III
GOMOS
SCIAMACHY
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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IMPORTANCE OF STRATOSPHERIC AEROSOL
•  Stratospheric aerosol is considered in total radiative forcing calculations and
is important to understand interannual variability.
•  It is currently understood to have contributed up to ¼ to the hiatus in global
warming after 1998 (Solomon et al., Science 2010).
NB, just
increase
from rising
methane is
considered
in these
models.
NB, lifetime
of longlived GHGs
is important
factor in
determining
radiative
forcing
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
IPCC AR5 (Figure 8-18), 2014
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SPARC DATA INITIATIVE AEROSOL
•  Quality-control and merging of
stratospheric aerosol products
is not straightforward due to the
wavelength dependency of
retrievals.
•  A new scaling approach
introduced in the SPARC Data
Initiative allows for an easier
comparison and may also be
used for merging.
Raw timeseries
Scaled timeseries
Hegglin et al., in preparation;
SPARC Data Initiative Report
(Eds. Hegglin & Tegtmeier), in print
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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STRATOSPHERIC OZONE
Tegtmeier et al, JGR 2013
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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IMPORTANCE OF STRATOSPHERIC OZONE
•  Total column ozone showed
no decline in the tropics.
WMO 2014, after Shepherd et al., Nature Geoscience 2014
•  However, decomposition into
tropospheric and stratospheric
column ozone reveals that
stratospheric ozone decline
was masked by an increase in
tropospheric ozone.
•  Provides independent
constraint on tropospheric
ozone, a major GHG but hard
to constrain from tropospheric
measurements
•  Comparison to limb sounder
measurements from the
SPARC Data Initiative was
crucial to prove model result.
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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STRATOSPHERIC WATER VAPOUR
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
1978
Hegglin et al, JGR 2013
LIMS
SAGE II
UARS-MLS
HALOE
POAM III
SMR(1)
SMR(2)
SAGE III
MIPAS
SCIAMACHY
ACE-FTS
Aura-MLS
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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IMPORTANCE OF STRATOSPHERIC H2O
•  Water vapour is the most important natural greenhouse gas in the atmosphere
and provides a positive feedback to the climate forcing from CO2.
•  A stratospheric water vapour trend of 0.4 ppmv/decade (as was apparently observed
over Boulder) over 1980-1997 would have led to global surface warming that was 44%
of that from CO2 alone.
•  The assumed constant water vapour increase induces a strong latitudinal structure in
the cooling of the stratosphere ! important for dynamical feedbacks
Changes are
largest in the
UTLS
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
Forster & Shine, GRL 1999
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THE STRATOSPHERIC H2O PUZZLE
Hurst et al., JGR 2011
•  At most one-third of the
observed trend over
Boulder can be
explained by CH4
oxidation.
Wang, Seidel & Free, JGR 2012
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
•  Also, tropical
tropopause
temperatures,
understood to be the
main other driver of
stratospheric water
vapour changes, show
rather a negative or
zero trend.
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NEW MERGING APPROACH
LEADS TO NEW ANSWERS
•  Bias-correct the data records
relative to MLS, using
CMAM30 as transfer function.
•  Result: homogenized time
series of stratospheric water
vapour, which can be merged.
•  Allows extension of the water
vapour record back into the
late 1980s, based on SAGE II.
H2O [ppmv]
a
6
HALOE SCIAMACHY ACE-FTS
SAGE II MIPAS Aura-MLS SMR
5
4
2
with bias
3
2
1
0
-1
bias-corrected
•  Determine the offsets with
respect to CMAM30.
Tropical H2O @ 100 hPa
3
Diff H2O(obs-CMAM20) [ppmv]
•  CMAM30 (gray) compares
very well with SAGE II and
HALOE between 1996-2001.
7
1
b
c
0
-1
H2O-corrected [ppmv]
•  Large discrepancies are
seen between instruments.
8
Hegglin et al., Nature Geoscience 2014
6
d
5
4
3
2
Jan 90
Jan 95
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
Jan 00
Jan 05
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SANITY CHECK
Hegglin et al., Nature Geoscience 2014
•  Tropical water vapour and
temperature anomalies
(scaled with respect to their
interannual variability) show
a strong correlation.
•  Residuals (differences
between the scaled
variables) mostly fluctuate
around zero.
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
CMAM
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STRATOSPHERIC H2O CHANGES
(late 1980s to 2010)
Hegglin et al., Nature Geoscience 2014
•  Trends in the lower to
mid stratosphere are
seen to be negative, not
positive as would be
inferred from the
Boulder record!
•  In the upper
stratosphere, the trends
are positive.
•  The vertical structure in
the changes indicates
structural changes in the
Brewer-Dobson
circulation.
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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STRATOSPHERIC SF6
Tegtmeier et al, ESSD submitted
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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IMPORTANCE OF HALOCARBONS
AND FLUORINATED SPECIES
•  Long-lived tracers can
be used as age-of-air
indicators.
Stiller et al., ACP 2012
•  Trends derived from
MIPAS SF6
measurements between
2002-2010 for example
indicate a slowing of the
stratospheric circulation.
•  Difference from Hegglin
et al. (2014) is explained
by a difference in the
time periods considered.
! Note, need for long-term
observational records!
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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MERGING TEMPERATURE DATA RECORDS
•  Stratospheric temperatures
are a key indicator of
stratospheric changes.
Thompson et al., Nature 2012
•  Using a new merging
method (based on MIPAS
limb measurements as a
transfer function between
SSU and AMSU), the
extended SSU record
shows excellent
agreement with the CMIP5
model mean and trends
over 1980-2012.
•  There still remain issues
on the latitudinal structure
in temperature changes.
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
McLandress et al., ACP 2015
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FUTURE NEEDS ! CCI+
•  Improve and understand climate data records (CDRs) of stratospheric ECVs in
order to understand climate variability and trends and the mechanisms that drive
them ! support international assessments and contribute to GCOS goals
•  Should extend to stratospheric ECVs other than ozone.
•  Should improve data products that will be merged into CDRs (SPARC Data Initiative)
•  Perform inter-comparison of ECVs derived using different data sources and
merging approaches to gain confidence in the products and assess uncertainty.
•  Assess consistency of variability and trends in water vapour, ozone, aerosol and
temperature, including link to circulation changes (other ECVs).
•  Yields information on consistency between ECVs in terms of geophysical structure.
•  Yields info in terms of cross-talk in retrievals (e.g. strat. aerosol in SST retrievals)
•  Also important consideration for joint analysis of nadir and limb observations (CH4).
•  Need for limb satellite sounders to be able to extend ECVs into the future.
•  In absence of future limb measurements, can use ground-based measurements to
determine long-term changes, but need to test their representativeness using the
‘golden age’ of satellite limb sounders.
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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CHEMISTRY-CLIMATE COUPLING
•  Climate change is expected to lead to a strengthening of the stratospheric
circulation, which affects ozone and other trace gases.
•  The decrease in water vapour is expected to lead to a decrease in the surface
temperature response.
•  It is important to understand the magnitude of these radiative-chemical
couplings.
Hegglin and Shepherd, Nature Geoscience 2009
Nowack et al., Nature Climate Change 2014
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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COUPLING BETWEEN OZONE
AND TEMPERATURE
•  Ozone is strongly coupled to temperature
in the mid to upper stratosphere, and also
in the polar vortex.
•  A free-running version of the CMAM
chemistry-climate model is compared to a
version in data assimilation mode and
indicates that a better representation of
temperature improves the ozone field.
•  Shows the use of a model to quantify the
coupling.
Hegglin, unpublished work for CSA
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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•  Wavelength bands GCOS stratospheric ECVs of long-lived trace gases can be
detected in (based on SPARC Data Initiative instruments).
SPARC Data Initiative Report (Eds. Hegglin&Tegtmeier), in print
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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SATELLITE INSTRUMENT EVALUATION
Hegglin et al, JGR 2013
•  First study to show that
SAGE II has a decent
H2O product.
•  Key point: opportunity
to extend the satellite
water vapour record
backward in time!
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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COMPARISON WITH BOULDER RECORD
CMAM30 and satellite mean have been shown to yield consistent results, with a
strong correlation between temperatures and water vapour.
H2O diff [ppmv]
H2O anomaly [ppmv]
1.0
a
0.5
Satellites merged
CMAM30
0.0
-0.5
-1.0
1.0
0.5
Boulder in-situ
b
CMAM30-subsampled
0.0
-0.5
-1.0
Jan 80
Jan 85
Jan 90
Jan 95
Jan 00
Jan 05
Jan 10
Although short-term fluctuations agree better, the long-term trend cannot be
reconciled with either the model or the satellite record.
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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PREDICTION OF FUTURE TRENDS
•  Stratospheric water vapour is predicted to increase by about 1 ppmv by the end of
the 21st century.
•  However stratospheric chemistry-climate models (CCMVal) do not agree on the
trend over the past 50 years.
Gettelman, Hegglin et al., JGR 2010
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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• 
The ozone hole thereby affects tropospheric surface climate during austral
summer outside SH high latitudes, e.g. in the tropics.
Jet
latitude
ozone
depletion
1960-2000
Hadley
cell width
ozone
recovery
2000-2050
Son et al., JGR 2010
(also McLandress et al.,
JClim 2011
• 
The ozone-hole induced surface wind changes have potential implications
for ocean circulation and carbon uptake (Cai & Cowan, J Clim 2007; Lenton
et al., GRL 2009)
ESA Climate Change Initiative Collocation meeting – ESRIN October 2015
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